Severe Leg Length Discrepancy after Total Hip Arthroplasty: Where is the Problem- Cup or Stem? A Retrospective Controlled Study

Abstract

Background: The factors that contribute to the severe leg length discrepancy (LLD) after total hip arthroplasty (THA) are presently unclear. In the current study, we investigated whether the acetabular cup position and femoral stem are related to the patients with severe LLD by comparing with patients who had the leg length equality.Materials and Methods: Between June 2013 and July 2019, patients undergoing unilateral primary THA in the Department of Orthopaedics at our institution were screened. According to the postoperative leg length difference, a total of 178 patients were included in the study. A group of 107 patients had leg length equality (LLD≤3 mm) and the other group of 71 patients had severe LLD (LLD≥15 mm). A standardized protocol for evaluation of anteroposterior hip radiographs was used to measure the postoperative LLD. The difference of acetabular cup position (vertical centre of rotation (VCR), horizontal centre of rotation (HCR)) and the femoral stem(stem height; stem size; femoral neck osteotomy level) between the two groups. We also assessed whether there was a difference in proximal femur morphology between the two groups.Results: On the femoral side, the mean stem height of (70.82±5.49) mm in the severe LLD group was significantly different from the (67.35±6.88) mm mean discrepancy in the leg length equality group (P < .001). Stem size and femoral neck osteotomy level showed no statistically differences between the two groups (P>0.05). On the acetabular side, there was no significant difference between the two groups in the VCR and HCR (P>0.05) . There was also no statistical difference in proximal femur morphology between the two groups (P>0.05).Conclusion: The main reason for the occurrence of severe LLD may be due to improper treatment of the femur side. Although preoperative template could choose a better stem size and femoral neck osteotomy level, surgeons need to pay more attention to the whole operation process of the femur stem.